It is well known to include in various kinds of imaging elements, a transparent layer containing magnetic particles dispersed in a polymeric binder. The inclusion and use of such transparent magnetic recording layers in light-sensitive silver halide photographic elements has been described in U.S. Pat. Nos. 3,782,947; 4,279,945; 4,302,523; 5,217,804; 5,229,259; 5,395,743; 5,413,900; 5,427,900; 5,498,512; and others. Such elements are advantageous because images can be recorded by customary photographic processes while information can be recorded simultaneously into or read from the magnetic recording layer by techniques similar to those employed for traditional magnetic recording art.
The transparent magnetic recording layer must be capable of accurate recording and playback of digitally encoded information repeatedly on demand by various devices such as a camera or a photofinishing or printing apparatus. The layer also must exhibit excellent running, durability (i.e., abrasion and scratch resistance), and magnetic head-cleaning properties without adversely affecting the imaging quality of the photographic elements. However, this goal is extremely difficult to achieve because of the nature and concentration of the magnetic particles required to provide sufficient signal to write and read magnetically stored data and the effect of any noticeable color, haze or grain associated with the magnetic layer on the optical density and granularity of the photographic elements. These goals are particularly difficult to achieve when magnetically recorded information is stored and read from the photographic image area. Further, because of the curl of the photographic element, the magnetic layer must be held more tightly against the magnetic heads than in conventional magnetic recording in order to maintain planarity at the head-media interface during recording and playback operations. Thus, all of these various characteristics must be considered both independently and cumulatively in order to arrive at a commercially viable photographic element containing a transparent magnetic recording layer that will not have a detrimental effect on the photographic imaging performance and still withstand repeated and numerous read-write operations by a magnetic head.
Problems associated with the generation and discharge of electrostatic charge during the manufacture and use of photographic film and paper have been recognized for many years by the photographic industry. The accumulation of charge on film or paper surfaces leads to the attraction of dust, which can produce physical defects. The discharge of accumulated charge during or after the application of the sensitized emulsion layers can produce irregular fog patterns or static marks in the emulsion. The severity of the static problems has been exacerbated greatly by the increases in sensitivity of new emulsions, increases in coating machine speeds, and increases in post-coating drying efficiency. The charge generated during the coating process results primarily from the tendency of webs of high dielectric constant polymeric film base to undergo triboelectric charging during winding and unwinding operations, during conveyance through the coating machines, and during post-coating operations such as slitting, perforating, and spooling. Static charge can also be generated during the use of the finished photographic product. For example, in an automatic camera, because of the repeated motion of the photographic film in and out of the film cassette, there is the added problem of the generation of electrostatic charge by the movement of the film across the magnetic heads and by the repeated winding and unwinding operations, especially in a low relative humidity environment. The accumulation of charge on the film surface results in the attraction and adhesion of dust to the film. The presence of dust not only can result in the introduction of physical defects and the degradation of the image quality of the photographic element but also can result in the introduction of noise and the degradation of magnetic recording performance (e.g., S/N ratio, "drop-outs", etc.). This degradation of magnetic recording performance can arise from various sources including signal loss resulting from increased head-media spacing, electrical noise caused by discharge of the static charge by the magnetic head during playback, uneven film transport across the magnetic heads, clogging of the magnetic head gap, and excessive wear of the magnetic heads. In order to prevent these problems arising from electrostatic charging, there are various well known methods by which an electrically-conductive layer can be introduced into the photographic element to dissipate any accumulated electrostatic charge.
Antistatic layers containing electrically-conductive agents can be applied to one or both sides of the film base as subbing layers either beneath or on the side opposite to the silver halide emulsion layers. An antistatic layer also can be applied as an outer layer coated either over the emulsion layers or on the side opposite to the emulsion layers or on both sides of the film base. Typically, in photographic elements of prior art comprising a transparent magnetic recording layer, the antistatic layer was preferably present as a backing layer underlying the magnetic recording layer.
The use of such electrically-conductive layers containing suitable semi-conductive metal oxide particles dispersed in a film-forming binder in combination with a transparent magnetic recording layer in silver halide imaging elements has been described in the following examples of the prior art. Photographic elements including a transparent magnetic recording layer and a transparent electrically-conductive layer containing fine granular particles of a semi-conductive crystalline metal oxide such as zinc oxide, titania, tin oxide, alumina, indium oxide, silica, complex or compound oxides thereof, both located on the backside of the film base have been described in U.S. Pat. Nos. 5,147,768; 5,229,259; 5,294,525; 5,336,589; 5,382,494; 5,459,021; and others. Of these conductive metal oxides, antimony-doped tin oxide is preferred. A wide variety of polymeric binders are indicated as suitable for use in the electrically-conductive layer of the photographic element, with gelatin and cellulose triacetate being the binders most commonly taught. Suitable binders for the magnetic layer are indicated to be thermoplastic resins having a T.sub.g in the range of from -40.degree. C. to 150.degree. C. in '768, '259, '589, and '021. U.S. Pat. Nos. 5,294,525 and 5,382,494 indicate suitable thermoplastic resins having a T.sub.g in the range of from -40.degree. C. to 180.degree. C. and a preferred range of 40.degree. C. to 150.degree. C. Vinyl chloride resins and cellulose derivatives such as cellulose nitrate, cellulose diacetate, and cellulose triacetate are typically indicated as the preferred thermoplastic resins for use in the magnetic layer. In addition hydrophilic binders such as gelatin are suitable. Photographic elements including a transparent magnetic recording layer and a transparent electrically-conductive layer containing zinc antimonate or indium antimonate, both located on the backside of the film base have been described in U.S. Pat. No. 5,457,013.
Photographic elements including an electrically-conductive layer containing colloidal vanadium pentoxide and a transparent magnetic recording layer have been disclosed in U.S. Pat. Nos. 5,395,743; 5,427,900; 5,432,050; 5,498,512; 5,514,528 and others. The preferred binder for the magnetic layer in the above U.S. Patents is cellulose diacetate. Vinylidene chloride containing polymers are disclosed as a preferred binder for electrically-conductive layers containing colloidal vanadium oxide. U.S. Pat. No. 5,514,528 also teaches an antistatic layer composed of colloidal vanadium oxide and an aqueous dispersible polyester coated on a subbed polyester support and subsequently overcoated with a transparent magnetic recording layer containing cellulose acetate. Conductive layers containing colloidal vanadium pentoxide prepared as described in U.S. Pat. No. 4,203,769 can exhibit low surface resistivities at very low weight fractions and dry weight coverages of vanadium oxide, low optical losses, and excellent adhesion of the conductive layer to film supports. However, colloidal vanadium pentoxide readily dissolves at high pH in developer solution during wet processing and must be protected by a nonpermeable, overlying barrier layer. The magnetic layer inherently can serve as a nonpermeable barrier layer, when overlying a conductive layer containing colloidal vanadium oxide. However, if the magnetic layer contains a high level of reinforcing filler particles, such as gamma aluminum oxide or silica fine particles, it must be crosslinked using suitable cross-linking agents in order to preserve the desired barrier properties, as taught in U.S. Pat. No. 5,432,050.
Alternatively, a film-forming sulfopolyester latex or polyesterionomer binder can be combined with the colloidal vanadium pentoxide in the conductive layer to minimize degradation during processing as taught in U.S. Pat. Nos. 5,360,706; 5,380,584; 5,427,835; 5,576,163; and others. Furthermore, it is disclosed that the use of a polyesterionomer can improve solution stability of colloidal vanadium pentoxide containing dispersions. Instability of vanadium pentoxide gels in the presence of various binders is well known and several specific classes of polymeric binders have been identified for improved stability or coatability, for example in U.S. Pat. Nos. 5,427,835; 5,439,785; 5,360,706; and 5,709,984. U.S. Pat. No. 5,427,835 teaches the use of sulfopolymers in combinations with vanadium oxide preferably prepared from hydrolysis of oxoalkoxides for antistatic applications. Sulfopolymers indicated to be useful include sulfopolyester, ethylenically-unsaturated sulfolpolymers, sulfopolyurethanes, sulfopolyurethane/-polyureas, sulfopolyester polyols, sulfopolyols, sulfonate containing polymers such as poly(sodiumstyrene sulfonate) and alkylene oxide-co-sulfonate containing polyesters.
U.S. Pat. No. 5,718,995 teaches an antistatic layer containing an electrically-conductive agent and a specified polyurethane binder having excellent adhesion to polyester supports and to an overlying transparent magnetic layer. The specified polyurethane is an aliphatic, anionic polyurethane having an ultimate elongation to break of at least 350 percent, however, sulfonated polyurethanes are neither taught nor claimed. Comparative Example 1 of '995 demonstrates that it is difficult to achieve adequate adhesion to glow discharge treated polyethylene naphthalate for a magnetics backing package composed of a solvent coated cellulosic-based magnetic layer and an antistatic layer containing colloidal vanadium pentoxide and either a sulfopolyester or interpolymer of vinylidene chloride cited as preferred binders in the above mentioned U.S. Patents. It was further demonstrated in Comparative Examples 9-13 that electrically-conductive layers composed of a non-preferred polyurethane binder also did not provide adequate adhesion. Electrically-conductive agents taught for use in combination with the specified polyurethane binder included tin oxide, colloidal vanadium oxide, zinc antimonate, indium antimonate and carbon fibers. It was further disclosed that electrically-conductive polymers as exemplified by polyanilines and polythiophenes may also be used. However, it was indicated that a coating composition consisting of the specified polyurethane binder and colloidal vanadium oxide had limited shelf-life (less then 48 hrs). Similarly, copending and commonly assigned U.S. Ser. No. 09/172,897 discloses as Comparative Examples unacceptable solution stability for electrically-conductive layers containing a non-sulfonated polyurethane binder and either polypyrrole or colloidal vanadium oxide.
The use of crystalline, single-phase, acicular, conductive metal-containing particles in transparent conductive layers for various types of imaging elements also containing a transparent magnetic recording layer has been disclosed in U.S. Pat. No. 5,731,119. Preferred binders include gelatin, aqueous dispersed polyurethanes, polyesterionomers, cellulose derivatives, and vinyl-containing copolymers. Preferred binders for the magnetic layer include gelatin, polyurethanes, vinyl-chloride based copolymers and cellulose esters, particularly cellulose diacetate and cellulose triacetate. Comparative Example 7 of '119 indicates poor adhesion for a magnetic layer containing cellulose diacetate and cellulose triacetate overlying an electrically-conductive layer containing granular tin oxide particles dispersed in a sulfonated polyester, AQ55D commercially available from Eastman Chemicals.
The use of electronically-conductive polythiophenes in an electrically-conductive layer either below or above a transparent magnetic layer is taught is U.S. Pat. No. 5,443,944. Suitable polythiophenes are prepared by oxidative polymerization of thiophene in the presence of polymeric carboxylic acids or polymeric sulfonic acids. Examples of polythiophene-containing antistatic layers either had no polymeric film-forming binder, a vinylidene chloride based terpolymer, or a polyurethane. The polyurethane binder was indicated to give "insufficient antistatic effects." Binders for the magnetic layer included cellulose triacetate, polymethylmethacrylate and polyurethane.
An electrically-conductive layer containing poly(3,4-ethylene dioxypyrrole/styrene sulfonate) in a film-forming binder used in combination with a transparent magnetic layer is claimed in U.S. Pat. No. 5,665,498. Similarly, an electrically-conductive layer containing polypyrrole/poly(styrene sulfonic acid) used in combination with a transparent magnetic layer is disclosed in U.S. Pat. No. 5,674,654. Suitable film-forming binders are indicated to include aqueous dispersions of polyurethanes or polyesterionomers. However, neither polyurethane film-forming binders nor a transparent recording layer overlying the electrically-conductive layer are taught. Sulfonated polyester binders as taught in '498 and '654 have resulted in insufficient adhesion to an overlying cellulosic magnetic layer as disclosed in copending and commonly assigned U.S. Ser. No. 09/172,897.
U.S. Pat. No. 5,707,791 claims a silver halide element having a resin layer composed of an antistatic agent and an aqueous-dispersible polyester resin or an aqueous-dispersible polyurethane resin, and magnetic layer coated on the resin layer. The antistatic agent is selected from a conductive polymer and a metal oxide. Suitable methods of making the polyurethane water dispersible are disclosed to include introducing a carboxyl group, sulfone group or tertiatry amino group into the polyurethane. Furthermore, the conductive polymers indicated are preferably anionic or cationic ionically-conducting polymers. Electronically-conducting polymers such as polythiophenes, polyanilines, or polypyrroles are not indicated. Thermoplastic resin suitable as polymeric binders for the magnetic layer are disclosed to have a T.sub.g of from -40.degree. C. to 150.degree. C. Preferred polymeric binders are cellulose esters, and more specifically cellulose diacetate is particularly preferred.
U.S. Pat. No. 5,382,494 claims a silver halide photographic material having a magnetic recording layer on a backing layer. The backing layer contains inorganic particles of a metal oxide which have at least one surface being water-insoluble, and dispersed in a binder in a proportion of 75.0% to 660% by weight of the binder. Suitable binders include a polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin and a polyester resin. It is further disclosed that "the backing layer is allowed to contain an organic particles in place of the inorganic particles." Suitable thermoplastic resins to be used as the polymeric binder for either the electrically-conductive layer or magnetic layer are to have a T.sub.g within the range of -40.degree. C. to 180.degree. C., and preferably 30.degree. C. to 150.degree. C.
U.S. Pat. No. 5,294,525 discloses a silver halide photographic material containing a transparent magnetic layer, a conductive layer containing conductive particles and a binder. The binder for the conductive layer contains a polar functional group consisting of --SO.sub.2 M, --OSO.sub.3 M and --P(.dbd.O)(OM.sub.1)(OM.sub.2) wherein M is hydrogen, sodium, potassium, or lithium; M.sub.1 and M.sub.2 are the same or different and represent hydrogen, sodium, potassium, lithium, or an alkyl group. Suitable binder resins include polyvinyl chloride resins, polyurethane resins, polyester resins and polyethylene type resins. However, '525 additionally claims the binder for the magnetic layer contain a polar functional group indicated above. Suitable thermoplastic resins for the binder of the magnetic layer are those which have a softening point of 150.degree. C. or less, an average molecular weight of 10,000 to 200,000 and a degree of polymerization of 200 to 2000. The required addition of a polar functional group in the binder of the magnetic layer is undesirable for the physical and chemical properties of the magnetic layer. Furthermore, increased permeability of the magnetic binder can potentially result in chemical change of the magnetic particles and consequently alter the desired magnetic signal. In addition, the barrier properties of the magnetic layer can be degraded by the addition of polar functional groups.
Because the requirements for an electrically-conductive layer to be useful in an imaging element are extremely demanding, the art has long sought to develop improved conductive layers exhibiting a balance of the necessary chemical, physical, optical, and electrical properties. As indicated hereinabove, the prior art for providing electrically-conductive layers useful for imaging elements is extensive and a wide variety of suitable electroconductive materials have been disclosed. However, there is still a critical need in the art for improved conductive layers which can be used in a wide variety of imaging elements, which can be manufactured at a reasonable cost, which are resistant to the effects of humidity change, which are durable and abrasion-resistant, which do not exhibit adverse sensitometric or photographic effects, which exhibit acceptable adhesion to overlying or underlying layers, which exhibit suitable cohesion, and which are substantially insoluble in solutions with which the imaging element comes in contact, such as processing solutions used for photographic elements. Further, to provide both effective magnetic recording properties and effective electrical-conductivity for an imaging element, without impairing its imaging characteristics, poses a considerably greater technical challenge.
The above indicated U.S. Patents could provide several advantages, e.g., improved solution stability, good conductivity, and good adhesion to polyester supports, for a variety of electrically-conductive layers containg various conductive agents. However, it has also been indicated that adhesion of an overlying magnetic layer to sulfonated polymers may be insufficient for several applications. Consequently, it is toward the objective of providing a useful combination of a transparent magnetic recording layer and an electrically-conductive layer which can be comprised of a wide variety of electrically-conductive agents and have acceptable adhesion to underlying and overlying layers that more effectively meet the diverse needs of imaging elements, especially those of silver halide photographic films, but also of a wide variety of other types of imaging elements than those of the prior art that the present invention is directed.